Here are some options for pre-tax retirement funds (ex. 401k):
1. Exchange your market-cap funds for S&P 500. Afaict, even with their own rules changing, they will wait up to 6 months (as opposed to 12) to let SpaceX in. This is the simplest solution that buys you time without losing other gains in the market, assuming your existing funds were broad market-cap funds. The idea here is to wait for ~5 months and see if you still want/need to exit S&P before they let SpaceX in, or pick another option.
2. Exchange your market-cap funds for RSP, an equal-weight fund. This is also simple and reduces your risk, as SpaceX's allocation of the fund would only be 0.2%.
3. Exchange your market-cap funds for a selection of different funds in order to replicate the previous allocation. Buy small-cap and mid-cap funds, and buy ETFs that cover the market without including tech. This is more complicated, but not really that complicated once you learn how to exchange funds. Still mostly passive, you're just actively managing your allocation into different indexes. Downside is you lose the gains from tech.
4. Exchange all your index funds - temporarily - for a money market fund or other low-risk, low-return investment vehicle, until SpaceX price settles down. This is the absolute simplest option, least risk, least reward. You lose all the gains from the market during this time, but a percentage of your fund doesn't disappear overnight. If you're nervous, it's safe to do this by June 11th and sit on it until July 5th and see what you'd like to do then.
You probably DO NOT want to do this for non-retirement funds, as you will get hit with capital gains taxes. You would have to estimate how much you think your portfolio would drop due to SpaceX's overinflated price falling, and compare that to your potential tax bill from rebalancing. It's almost certain that your tax hit would be higher.